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Monitoring Tunnels

Is there a good way to monitor GRE tunnels? I use software that pages me when an interface goes down. I have noticed when the far end of a GRE tunnel goes down the near end shows “tunnel46 UP, Line Protocol UP”. If this is normal behavior than how do you monitor tunnels?

Hall of Fame Super Silver

Re: Monitoring Tunnels


What you describe is indeed the traditional behavior of GRE tunnels, the tunnel interface will show up/up even when there is not end to end connectivity. Cisco has recently introduced a feature to address this. It is GRE tunnel keepalives. If you are running code that is recent enough you can enable the keepalives and then the GRE tunnel should act like other kinds of interfaces and if it loses end to end connectivity the tunnel interface should go protocol down. This would allow your monitoring software to treat them like other kinds of interfaces.

Note: even though I deal with lots of GRE tunnels I have only experimented with this in a lab environment, so I can not speak from experience about how it works. It worked well in the lab.